The present invention relates to a multi-piece solid golf ball. More particularly, it relates to a multi-piece solid golf ball having very soft and good shot feel at the time of hitting, and having high rebound characteristics and excellent flight performance, while maintaining good productivity and the like.
Golf balls, which are commercially selling, are typically classified into thread wound golf balls and solid golf balls. In the solid golf balls, a two-piece solid golf ball composed of a core and a cover covering the core, and a multi-piece solid golf ball, such as a three-piece solid golf ball comprising an intermediate layer between the core and the cover of the two-piece solid golf ball, generally occupy the greater part of the golf ball market. The multi-piece solid golf ball has excellent flight performance and good shot feel at the time of hitting, because of accomplishing various hardness distributions as compared with the two-piece golf ball. There has been no golf ball, which has high rebound characteristics and excellent flight performance when hit by all golfers, such as golfers who swings the golf club at low head speed, golfers who swings the golf club at high head speed and the like.
In a conventional multi-piece golf ball, the intermediate layer has been typically formed from rubber material or thermoplastic resin as main component. If formed from rubber material, the rubber composition comprising high-cis polybutadiene, zinc salt of (meth)acrylic acid, peroxide curing agent and other additive typically is used as the rubber material. The zinc salt of (meth)acrylic acid acts as a co-crosslinking agent to form not only oxygen crosslink with peroxide in rubber molecular, but the other crosslink with the zinc (meth)acrylate between rubber moleculars, whereby improving flight performance and shot feel at the time of hitting of the resulting golf ball.
In the multi-piece golf ball comprising the intermediate layer, it is important that the core is soft and the intermediate layer has high hardness in order to accomplish both soft and good shot feel and excellent flight performance. However, since the thickness of the intermediate layer is typically very small, it is difficult to accomplish the sufficient hardness of the intermediate layer to impart high rebound characteristics and excellent flight performance to the resulting golf ball by using the co-crosslinking agent. There has been problem that the releasability is largely degraded, and the productivity is degraded, if increasing the amount of the co-crosslinking agent in order to heighten the hardness of the intermediate layer.
It has been proposed to use a blend of the zinc (meth)acrylate and an unsaturated carboxylic acid ester as a co-crosslinking agent in the rubber composition for a one-piece solid golf ball or a center of a multi-piece solid golf ball in order to accomplish high hardness (for example, in Japanese Patent Kokai publication Nos. 25337/1982, 80068/1990).
A composition for solid golf ball comprising 20 to 35 parts by weight of a mixture of multi-functional unsaturated ester and unsaturated carboxylic acid as a polymerization crosslinkable monomer, based on 100 parts by weight of polybutadiene, is described in Japanese Patent Kokai publication No. 25337/1982. It is also described to use the composition for an integrally molded solid golf ball (one-piece golf ball) or a center of a multi-piece solid golf ball. However, since the amount of the mixture of multi-functional unsaturated ester and unsaturated carboxylic acid in the composition is small, the molding article is soft, and sufficient rebound characteristics are not obtained. In the integrally molded solid golf ball or the center of the multi-piece solid golf ball using the composition, the surface hardness is low, and sufficient flight performance of the resulting golf ball is not obtained.
A solid golf ball comprising a core formed from a vulcanizing article of rubber composition comprising 7 to 14 parts by weight of a metal salt of unsaturated carboxylic acid, 5 to 30 parts by weight of an unsaturated carboxylic acid ester of not less than pentavalent alcohol or epoxy resin and 1 to 5 parts by weight of organic peroxide, based on 100 parts by weight of polybutadiene, is described in Japanese Patent Kokai publication No. 80068/1990. Since the amount of the metal salt of unsaturated carboxylic acid and unsaturated carboxylic acid ester is large, high hardness is obtained. However, the core is hard, and soft shot feel is not obtained. The crosslinking is not sufficiently conducted, and high rebound characteristics are not obtained, because the amount of the metal salt of unsaturated carboxylic acid is small.
There has been no golf ball, which is sufficient to accomplish the balance between shot feel at the time of hitting and flight performance. It has been required to provide the golf ball, which the flight performance and the shot feel are improved still more without the deterioration of the other performance such as the productivity.
A main object of the present invention is to provide a multi-piece solid golf ball having very soft and good shot feel at the time of hitting, and having high rebound characteristics and excellent flight performance, without the deterioration of the other performance such as the productivity.
According to the present invention, the object described above has been accomplished, in a multi-piece solid golf ball comprising a core consisting of a center and at least one layer of intermediate layer formed on the center, and a cover covering the core, by using a rubber composition comprising a specified amount of xcex1,xcex2-unsaturated carboxylic acid or metal salt thereof and xcex1,xcex2-unsaturated carboxylic acid ester in at least one layer of the intermediate layer, thereby providing a multi-piece solid golf ball having very soft and good shot feel at the time of hitting, and having high rebound characteristics and excellent flight performance, without the deterioration of the other performance such as the productivity.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.